Dear all,
I would have some simple questions regarding "fully balanced" and push-pull amplifiers, can you please help ?
- a single ended amplifier has (usually) 1 output device, ON during the full 360° cycle of the input signal, right ?
- a push-pull amp has at least 2 output devices, each ON only for 1 half of the signal cycle, exactly 180° in class B and with some overlap in class AB (180°+) to avoid crossover distortion, right ?
- in push-pull, during the overlap both output devices conduct. The wider this region is set, the more first Watts are going to operate in pure Class A mode, right ? And the less maximum output the pair has.
- How about Class A pushpull ? (I've seen some). At least 2 devices, but which conducts how long ? Both output devices ON for 360° while signal is fed once to one part and then once to the other ? How does it look power-wise ? (I think it's not the same like parallelling tubes in SE config. This is real pushpull too, but remains Class A all the time).
Let's take a fully balanced mono amplifier topology (end-to-end) with XLR input. XLR Pin1 is ground, Pin2 is hot signal and Pin3 is cold signal, the inverse of Pin2.
- We then take both signals and amplify them with 2 single-ended preamp+output chains, right ?
- Normal signal gets amplified with 1 output device, inverted signal gets amplified with another output device and we sum these signals then on the output to have the overall signal level doubled while rejecting all common mode noise, including common mode noise picked up by the XLR cable and also including all cm noise picked up inside the amp, right ? So at the very end, all common mode noise are eliminated and here we go, a fully-balanced amplifier. But this is still SE, so Class A, made with 2 devices.
- In order to build a push-pull Class AB fully balanced amp, we need to amplify both XLR Pin2 and XLR Pin3 signals via a push-pull chain, which means 4 output devices altogether, right ? Still for 1 monoblock. First the pushpull parts get into one whole signal on both normal and inverted sides, then there's still another connection of these now-complete sides to get the balanced effect, am I right ?
- None of the above is to be confused with bridged mode operation, right ? That's again something different, regardless of balanced/unbalanced/SE/PP topics if I'm correct and for all of these operations there's a bridged mode if parts can bear that.
. 
